The present invention relates to a fuel intake system for a supercharged automotive engine.
A supercharged engine, especially a turbocharged engine, is currently known which includes a turbocharger comprised of a turbine and a compressor driven by the turbine for increasing the amount of air-fuel mixture delivered to the engine. With the turbocharger, it is possible to boost the engine power output and also to increase the automobile mileage per gallon of fuel.
In this prior art supercharged engine, it has been found that the temperature of the air-fuel mixture to be delivered to the engine tends to increase during the operation of the supercharger. This is because, while the air-fuel mixture being compressed by the compressor of the supercharger is heated, the air-fuel mixture is further heated when mixed with a high temperature, dilution gas, i.e., a portion of exhaust gases remaining inside the engine and which has not been completely exhausted. The increased temperature of the air-fuel mixture is often-times liable to increase the temperature and pressure inside the engine which tend to constitute a cause of the occurrence of engine knocking.
The increase of the temperature of the supercharged air-fuel mixture can be minimized by lowering the performance of the supercharger compressor, but this technique is counter to the maximum utilization of the supercharger.
Alternatively, it may also be minimized by the use of a cooler for cooling the supercharged air-fuel mixture prior to it being delivered to the engine, such as disclosed in, for example, in the U.S. Pat. No. 4,010,613, patented Mar. 8, 1977.
Although the specification of the above listed U.S. Patent is silent as to whether or not the possibility of occurrence of the engine knocking can be minimized, it describes that the engine combustion temperature can be lowered thus minimizing the production of obnoxious oxides of nitrogen in the engine exhaust. In any event, although it appears that the lowering of the engine combustion temperature such as achieved in the above listed U.S. Patent is effective to minimize the occurrence of the engine knocking as well, the use of the cooler renders the engine fuel intake system complicated and costly.
In order to minimize the occurrence of the engine knocking without relying on the cooler such as used in the, above listed U.S. Patent, it can be contemplated to open the fuel intake port at a time shortly before the closure of an exhaust port so that the supercharged air-fuel mixture can, as it enters the engine cylinder through the fuel intake port, expel the dilution gas out of the engine cylinder through the exhaust port which has not yet been closed. This may be effective where the engine is operated under a high load operating condition, but this contemplated method poses a problem particularly when the engine is operated under a low load operating condition during which the supercharger is generally brought to a halt. Specifically, during the low load engine operating condition, the air-fuel mixture to be delivered to the engine is not supercharged and is under a pressure lower than the exhaust gas pressure. Therefore, the dilution gas tends to remain inside the engine cylinder in so large an amount as to result in reduction in combustibility and also in drivability of the engine.